In the present patent application, an active array antenna architecture is said to be of ‘tile’ type if its active components, notably its amplifiers and its phase shifters, are disposed in planes parallel to the radiating plane, so as to obtain a mechanically orientable antenna of restricted depth or one that can be installed on the surface of a carrier.
The radiating elements of such an array antenna can be grouped into sub-arrays of 2n radiating elements (where n is a positive integer), called ‘elementary tiles’. Indeed, the pitch of the array, that is to say the distance between the center of 2 neighboring radiating elements, generally around λ/2 for an electronic-scanning antenna (where λ designates the wavelength of the radiated wavebeam), is much too small to embed the components required for individual control of the radiating elements. The radiating elements of an elementary tile are disposed row-wise (or column-wise) perpendicularly to the antenna scan plane and are connected to a distributor consisting of Wilkinson dividers of restricted proportions whose input is linked to an active pathway of the antenna. The surface area of 2, 4 or 8 radiating elements is thus available for embedding the active and passive components required to constitute an active pathway. The pitch of the array must however be widened, up to about 0.65λ, so as to obtain a sufficient area to allow the active pathways to be housed in a metal casing and the mechanical play which is indispensable for an array-like assemblage, while being compatible with the intended beam scan field.
Unfortunately, such an array pitch limits the antenna's pointing performance, notably when it is desired to scan the beam in a plane along the orientation of the radiated electric field, this plane being called E subsequently.
A major drawback of the array-like arrangement of radiating elements of relatively significant dimensions, is that blind directions appear, that is to say directions in which it is not possible to scan the beam. A blind direction is related to the fact that, for a given frequency and a particular pointing, the active SWR (Standing Wave Ratio) at the input of each of the radiating elements attains a very high value, the reflection coefficient being close to 1. This phenomenon, which is destructive for the active circuits of the antenna, corresponds to the bringing into phase of the couplings between a large number of radiating elements and an arbitrary radiating element situated in the middle of the array of elements.